Andreev et al 2004 Boreas

Transcription

Late Saalian and Eemian palaeoenvironmental history of the Bol’shoy
Lyakhovsky Island (Laptev Sea region, Arctic Siberia)
ANDREI A. ANDREEV, GUIDO GROSSE, LUTZ SCHIRRMEISTER, SVETLANA A. KUZMINA, ELENA YU. NOVENKO,
ANATOLY A. BOBROV, PAVEL E. TARASOV, BORIS P. ILYASHUK, TATIANA V. KUZNETSOVA, MATTHIAS KRBETSCHEK,
HANNO MEYER AND VIKTOR V. KUNITSKY
Andreev, A. A., Grosse, G., Schirrmeister, L., Kuzmina, S. A., Novenko, E. Yu., Bobrov, A. A., Tarasov, P.
E., Ilyashuk, B. P., Kuznetsova, T. V., Krbetschek, M., Meyer, H. & Kunitsky, V. V. 2004 (November): Late
Saalian and Eemian palaeoenvironmental history of the Bol’shoy Lyakhovsky Island (Laptev Sea region,
Arctic Siberia). Boreas, Vol. 33, pp. 319–348. Oslo. ISSN 0300-9483.
Palaeoenvironmental records from permafrost sequences complemented by infrared stimulated luminescence
(IRSL) and 230Th/U dates from Bol’shoy Lyakhovsky Island (73°20'N, 141°30'E) document the environmental
history in the region for at least the past 200 ka. Pollen spectra and insect fauna indicate that relatively wet grasssedge tundra habitats dominated during an interstadial c. 200–170 ka BP. Summers were rather warm and wet,
while stable isotopes reflect severe winter conditions. The pollen spectra reflect sparser grass-sedge vegetation
during a Taz (Late Saalian) stage, c. 170–130 ka BP, with environmental conditions much more severe compared
with the previous interstadial. Open Poaceae and Artemisia plant associations dominated vegetation at the
beginning of the Kazantsevo (Eemian) c. 130 ka BP. Some shrubs (Alnus fruticosa, Salix, Betula nana) grew in
more protected and wetter places as well. The climate was relatively warm during this time, resulting in the
melting of Saalian ice wedges. Later, during the interglacial optimum, shrub tundra with Alnus fruticosa and
Betula nana s.l. dominated vegetation. Climate was relatively wet and warm. Quantitative pollen-based climate
reconstruction suggests that mean July temperatures were 4–5°C higher than the present during the optimum of
the Eemian, while late Eemian records indicate significant climate deterioration.
Andrei A. Andreev (e-mail: [email protected]), Guido Grosse, Lutz Schirrmeister, Hanno Meyer and
Pavel E. Tarasov, Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam,
Telegrafenberg A43, D-14473 Potsdam, Germany; Svetlana A. Kuzmina, Paleontological Institute, RAS
Profsoyuznaya 123, 117997 Moscow, Russia; Elena Yu. Novenko, Institute of Geography RAS, Staromonetny 29,
109017 Moscow, Russia; Anatoly A. Bobrov, Faculty of Soil Science Moscow State University, Vorobievy Gory,
119992 Moscow, Russia; Boris P. Ilyashuk, Institute of North Industrial Ecology Problems, Kola Science Center,
Russian Acadamy of Sciences, Fersman St. 14, 184200 Apatity, Russia; Tatiana V. Kuznetsova, Faculty of
Geology, Moscow State University, Vorobievy Gory, 119992 Moscow, Russia; Matthias Krbetschek, Saxon
Academy of Science, Quaternary Geochronology Section, Bernhard-von-Cotta-Str. 4, 09596 Freiberg, Germany;
Viktor V. Kunitsky, Permafrost Institute, Siberian Branch Russian Academy of Science Yakutsk, Russia; received
24th November 2003, accepted 7th July 2004.
Palaeoenvironmental, especially palynological, studies
have already been conducted on permafrost sections in
the Northern Yakutia (Rybakova 1962; Giterman 1976–
1977; Lozhkin 1977; Sher et al. 1977; Kaplina 1979;
Kaplina et al. 1978, 1980; Kaplina & Giterman 1983;
Tomirdiaro 1980; Barkova 1982, 1990; Rybakova &
Kolesnikov 1983; Rybakova & Pirumova 1986; Alekseev 1989, 1997; Makeyev et al. 1989, 2003; Igarashi et
al. 1995; Andreev et al. 2001, 2002a), but only a few of
them are relatively well dated and at a high resolution,
making the chronological correlation of the reconstructed environmental fluctuations difficult.
In 1998–2001 the permafrost sequences on the
Bykovsky Peninsula (Mamontovy Khayata site) and
north of the Chekanovsky Ridge (Buor-Khaya site)
were studied within the scope of the research project
‘Palaeoclimate signals in ice-rich permafrost’ established by the German–Russian science cooperation
‘Laptev Sea System’. These multidisciplinary studies
have greatly improved the knowledge of the Late
Quaternary environmental history of the region (e.g.
Andreev et al. 2002a; Meyer et al. 2002a; Schwamborn
et al. 2002; Krbetschek et al. 2002; Schirrmeister et al.
2002a, in press; Kienast 2002; Kuzmina 2002; Bobrov
et al. 2004). The Quaternary deposits of the southern
coast of Bol’shoy Lyakhovsky Island were first noted by
Bunge (1887) and Toll (1897). First detailed studies
were carried out much later by Romanovskii (1958a–c),
according to whom the deposits consist of lagoon and
flood-plain sediments. In contrast, Japanese researchers
propose that the Ice Complex deposits were formed in a
large swampy marshland on the dried Pleistocene
Laptev Sea shelf (Nagaoka 1994; Nagaoka et al.
1995), whereas Kunitsky (1998) considers them to be
formations connected with perennial snow patches on
cryoplanation terraces.
Discussions about the age of the studied deposits are
also controversial. According to Romanovskii (1958a,
b) their age varies from the Middle/Late Pleistocene (for
the oldest deposits) to the Holocene, whereas Arkhangelov et al. (1996), based on TL dates (980 250 ka
and 950 250 ka) and palaeomagnetic analyses, proDOI 10.1080/03009480410001974 # 2004 Taylor & Francis
320
Andrei A. Andreev et al.
BOREAS 33 (2004)
Fig. 1. A. Map of the Arctic. B. Map of the Laptev Sea – Bol’shoy Lyakhovsky Island region. 1 – Mamontovy Khayata site, 2 – Buor-Khaya
site. C. Study area on Bol’shoy Lyakhovsky Island.
Late Saalian and Eemian history, Laptev Sea region
BOREAS 33 (2004)
321
posed a late Pliocene/early Pleistocene age for the
lowest deposits.
Recent studies of permafrost sequences from a key
site situated on the southern coast of Bol’shoy
Lyakhovsky Island at the mouth of Zimov’e River
(Fig. 1) were also carried out within the scope of the
project ‘Palaeoclimate signals in ice-rich permafrost’.
New palaeoenvironmental records dated by 230Th/U,
IRSL and 14C methods document the environmental
oscillations in the region from at least c. 200 ka until the
present. This paper presents new palaeoenvironmental
reconstructions since an interstadial during the Taz
(Late Saalian) time, prior to 200 230Th/U ka ago up to
the Zyryanian (Early Weichselian) stage c. 60–70 ka
ago.
Fig. 2. The coastal section around Zimov’e river mouth and locations of studied profiles.
Study area
Large areas of the Bol’shoy Lyakhovsky Island are
covered by ice-rich permafrost deposits. A key site
located on the southern coast of Bol’shoy Lyakhovsky
Island on the Dmitri Laptev Strait (73°20'N, 141°30'E,
Fig. 1) was studied in summer 1999. This site consists of
coastal and thermoerosion cliffs up to 40 m high
extending for about 2.5 km to the east and about
3.5 km to the west from the Zimov’e River mouth
(Fig. 2).
The modern climate of the area is characterized by
long (8 months), severe winters with January temperatures of 31 to 32°C and short, cold summers with
July temperatures around 4°C and about 200 mm annual
precipitation (Atlas Arktiki 1985). Soils in the area are
mainly tundra-gley and peaty-gley (histosols and
inceptisols) with an active-layer thickness of about
30–40 cm (Atlas Arktiki 1985). Permafrost has a
thickness of 500–600 m (Grigoriev et al. 1996). The
area belongs to the northern tundra zone ( Atlas Arktiki
1985). Moss-grass–low-shrub tundra dominates the
vegetation, with vascular plant species such as Salix
pulchra, Cassiope tetragona, Dryas punctata, Oxyria
digyna, Alopecurus alpinus, Poa arctica, Carex ensifolia, C. rotundifolia and Eriophorum medium, mosses
such as Aulacomnium turgidum, Hylocomium alaskanum, Drepanocladus iniciatus and Calliergon sarmentosum and lichens such as Alectoria ochroleuca,
Cetraria cuculliata and C. hiascus.
The lowest (oldest) frozen soft rocks are periglacially
reworked remains of a yellowish to greenish coloured
Palaeogene weathering crust exposed at sea level
(Kunitsky et al. 2000). The overlaying unit (unit I)
contains ice-rich silty and silty-sandy deposits with
pebbles, peat inclusions and peat horizons. Ice belts,
lens-like reticulated interlayers and wide ice wedges
with symmetric shoulders are indicative of syngenetic
permafrost conditions. Unit I is suggested to be the
deposit of an old Ice Complex, similar to the Late
Pleistocene (Weichselian) Ice Complex formation that
322
BOREAS 33 (2004)
Table 1. Infrared stimulated luminescence (IRSL) dates from the lower units of the Zimov’e River key site.
Sample ID (altitude a.s.l.)
Annual dose rate (Gy/ka)
Palaeodose (Gy)
IRSL age (ka)
Lab no.
Unit
R17, 500 cm
R17, 750 cm
R1850-B11, 1290 cm
R1850-B13, 1470 cm
R985, 880 cm
R985, 1020 cm
R2260, 100 cm
R2260, 200 cm
2.63 0.43
3.66 0.65
3.70 0.64
Not datable
3.36 0.59
4.03 0.62
4.06 0.61
4.14 0.60
352 7.2
283.2 14.1
210.3 12.3
134 22
77 14
57 10
227.5 24
310.4 9.1
402 10.3
422.9 20.8
68 14
77 12
99 15
102 16
Lya-2
Lya-3b
Lya-4
Lya-5
Lya-8
Lya-9
Lya-10
Lya-11
Transition I to IV
IV
IV
IV
IV
IV
IIa
IIa
is widely distributed in northeastern Siberia. The next
unit (unit II) mostly forms the lower part of the coastal
cliff up to about 6 m a.s.l. Two different facies subunits
were observed. Unit IIa consists of well-sorted, homogenous loess-like fine-grained silty to sandy, relatively
ice-poor sediments with massive cryostructure containing numerous vertically orientated roots, small ice and
sand-ice wedges. Unit IIb consists of laminated, bluishgrey sediments containing numerous shells of the
freshwater molluscs (Pisidium sp., Sphaerium corneum,
Valvata piscinalis, Lymnaea cf. peregra) and freshwater
ostracods. Unit IIb is sinuously deformed (amplitude 2–
3 m, length 10–20 m) and sporadically covered by a
horizon of ice-wedge casts with laminated subaquatic
deposits (unit III). Younger loess-like deposits, very
similar to unit IIa, exposed between 3 and 15 m a.s.l.,
are considered as unit IV. They contain more ice as ice
belts and larger ice wedges. The subsequent Ice
Complex deposits (unit V) form steep walls up to
25 m high. This unit is composed of wide (up to 6 m)
and long (up to 25 m) ice wedges and sandy sediments
with numerous peat lenses and palaeosol horizons,
especially in the upper part. Unit V was formed during
the Late Pleistocene, between c. 55 and 30 ka BP
(Kunitsky 1996, 1998; Nagaoka et al. 1995; Meyer et
al. 2002). Holocene sediments (unit VI) of thermokarst
depressions and thermoerosional valleys as well as
modern soils cover the Ice Complex deposits in some
places. The stratigraphical succession of the studied
units appears to be repeatedly changed by thermoerosional and thermokarst processes and the refilling of
temporal depressions. Therefore, no complete profiles
containing unit I to unit VI could be observed.
Methods
The Zimov’e River key site was sampled for palaeoecological studies (pollen, beetles, rhizopods, chironomids), age determinations (IRSL, 230Th/U, 14C),
sedimentological, palaeomagnetic and ground-ice studies during fieldwork in 1999 (Kunitsky et al. 2000).
Several profiles were sampled (Fig. 2), starting from the
beach level, in order to study the oldest part of the
section. Samples were taken from cleaned and frozen
deposits. Owing to the cryolithological structure of the
Table 2. AMS radiocarbon dates from the lower units of the Zimov’e River key site.
Sample ID (altitude a.s.l.)
LYA-L14
S3, 420 cm
LYA-L14
S4, 540 cm
LYA-R17
S8, 670 cm
LYA-R850
S12, 90 cm
LYA-R850
S37, 300 cm
LYA-R1850B11
S2, 1270 cm
LYA-R1850Bj13
S6, 1375 cm
LYA-R1850Bj13
S8, 1350 cm
LYA-R985
S4, 900 cm
LYA-R1440
S8, 660 cm
Dated material
14
Lab no.
Unit
C age (ka BP)
Roots and twigs
Leached residues
>50 420
KIA 9895
IIb
Small roots and twigs
Leached residues
>50 880
KIA 9896
III
Plant detritus
Plant residues,
alkali residue
Plant residues,
alkali residue
Plant residues,
alkali residue
Plant residues
alkali residue
Plant residues,
alkali residue
Plant residues,
alkali residue
Plant residues,
alkali residue
Plant residues,
alkali residue
36 510
960/ 860
>53 250
KIA 12553
IV
KIA 14730
I
49 810
3150/ 2260
44 000
3430/ 2390
>54 050
KIA 14749
IV
KIA 12535
IV
KIA 12536
IV
>44 160
KIA 12537
IV
49 200
2400/ 1850
50 110
2950/ 2150
KIA 14731
IV
KIA 9891
IV
Moss
Plant remains
Wood and plant remains
Plant remains
Plant remains
Moss
Roots, wood, plant remains
Fig. 3. Cryolithological structure and pollen percentage diagram of section R17.
BOREAS 33 (2004)
323
Dominating ecological groups
No. of species (n)
or %
Total sum (n)
Arctic and typical tundra species (tt)
Chrysomelidae
Chrysolina tolli Jac.
Ch. subsulcata Mnnh.
Ch. wollosowiczi Jac.
Ch. bungei Jac.
Chrysolina sp.
Curculionidae
Isochnus arcticus Korot.
Mesic tundra species (mt)
Carabidae
Diacheila polita Fald.
Pelophila borealis Payk.
Blethisa catenaria Brown.
Pterostichus (Cryobius) spp.
P. (Cryobius) brevicornis (Kirby)
P. (Cryobius) pinguedineus Esch.
P. (Cryobius) ventricosus Esch.
P. (Steroperis) costatus Men.
P. (Steroperis) vermiculosus Men.
P. (Steroperis) agonus Horn.
Leiodidae
Cryocatops poppiusi Jeann.
Staphylinidae
Tachinus arcticus Motsch.
Olophrum consimile Gyll.
Byrrhidae
Simplocaria arctica Popp.
Curimopsis cyclopedia Muenst.
Chrisomelidae
Chrysolina septentrionalis Men.
Dry tundra species (dt)
Carabidae
Carabus (Morphocarabus) odoratus
Motsch.
Bembidion (Peryphus) dauricum Motsch.
Poecilus (Derus) nearcticus Lth.
Pterostichus (Petrophilus) magus Man.
P. (Petrophilus) tundrae Tschitsch.
P. (Petrophilus) montanus (Motsch.)
P. (Petrophilus) abnormis Sahlb.?
P. (Lyperopherus) sublaevis Sahlb.
P. (Stereocerus) haematopus Dej.
P. (Europhilus) eximus Mor.?
Curtonotus alpinus Payk.
Amara (s.s.) interstitialis Dej.
Trichocellus mannerheimi Sahlb.
Apionidae
Metatrichapion tschernovi T.-M.
Curculionidae
Sample ID (altitude, cm a.s.l.)
5
1
1
1
13
1
3
4
3
6
2
tt/mt/dt
%
26/52/12
42
1
1
3
3
8
1
tt/mt
n
9/9
21
1
1
tt/dt
n
1/1
2
6
3
4
1
3
tt/mt/dt
n
4/7/8
26
10
2
2
1
2
2
1
3
1
1
5
1
1
2
4
tt/mt/dt
n
8/11/5
25
1
dt/aq
n
1/1
3
2
1
3
1
1
mt/dt
n
4/3
9
3
1
45
1
2
1
2
11
2
1
1
2
2
5
1
1
1
9
4
4
4
1
6
4
2
1
1
2
mt/dt/aq
%
46/21/9
89
24
3
4
3
24
3
5
2
1
6
mt/dt/ss/st
%
36/30/15/6
199
1
1
na
n
2
7
1
23
3
3
1
2
3
1
8
1
2
1
1
1
1
1
1
2
1
6
1
1
1
8
8
2
mt/dt/na/ss
%
45/27/7/6
71
3
7
1
10
16
5
2
4
18
24
6
3
1
1
mt/dt/na/aq
%
45/19/10/8
217
2
1
17
1
1
2
25
3
3
8
4
tt/mt/dt
%
22/57/16
81
1
1
1
3
1
1
tt/mt/dt
n
5/2/9
19
R17-R4, R17R17- R1730- R1730- R1430- R1430- R22R22R22R221230- L12
L1230420
B2, 450 B1,520 R3, 320 R2,360 R5,400 R6,440 B13,120v B14, 240 B15, 250 B16,400 B18, 350 30-B17, 400 B19, 700
Table 3. List of beetle taxa found in Zimov’e River key site (for explanations of abbreviations of ecological groups, see 1st column).
324
BOREAS 33 (2004)
Sitona borealis Korot.
Hypera ornata Cap.
H. diversipunctata Schrank.
Meadow-steppe species (ms)
Carabidae
Harpalus vittatus kiselevi Kat. et Shil.
H. vittatus vittatus Gebl.
Melyridae
Troglocollops arcticus L. Medv
Curculionidae
Coniocleonus sp.
Meadow species (me)
Chrysomelidae
Bromius obscurus L.
Phaedon concinnus Steph.
Steppe species (st)
Carabidae
Cymimdus arcticus Kryzh. et Em.
Chrysomelidae
Chrysolina brunnicornis bermani Medv.
Curculionidae
Stephanocleonus eruditus Faust
S. fossulatus F.-W.
Sedge hearth species (ss)
Byrrhidae
Morychus viridis Kuzm. et Korot.
Species of xeric habitats (ks)
Carabidae
Notiophilus aquaticus L.
Scarabaeidae
Aphodius sp.
Species of shrub habitats (sh)
Chrysomelidae
Phratora sp.
Curculionidae
Lepyrus sp.
L. nordenskjoeldi Faust
Isochnus flagellum Erics.
Dorytomus sp.
Wet and riparian habitat species (na)
Carabidae
Nebria frigida Sahlb.
Elaphrus riparius L.
E. lapponicus Gyll.
Bembidion (Peryphus) sp.
B. (Peryphus) umiatense Lindrt.
Agonum sp.
A. impressum Panz.
Hydrophilidae
Cercyon sp.
Staphylinidae
Stenus sp.
Coccinellidae
Scymnus sp.
Chrysomelidae
Hydrothassa hannoverana F.
H. glabra Hbst
Curculionidae
Phytobius sp.
1
1
1
1
2
2
1
1
2
5
1
1
1
1
1
1
1
1
1
1
2
2
4
1
3
3
2
2
1
2
1
2
1
1
1
1
1
1
2
2
1
2
4
1
2
1
1
1
6
6
2
2
1
1
1
1
1
1
3
12
3
1
1
1
2
2
2
1
3
1
4
1
1
1
1
BOREAS 33 (2004)
325
1
1
1
1
1
1
1
2
1
1
1
1
2
2
1
1
1
1
3
1
1
2
1
1
1
1
1
2
1
1
3
2
1
1
1
7
6
2
1
1
1
1
2
R17-R4, R17R17R1730- R1730- R1430- R1430- R22R22R22R221230- L12
L1230420
B2, 450 B1,520 R3, 320 R2,360
R5,400
R6,440
B13,120v B14, 240 B15, 250 B16,400 B18, 350 30-B17, 400 B19, 700
Notaris bimaculatus F.
Heteroptera, Saldidae
Salda sp.
Aquatic species (aq)
Dytiscidae
Agabus sp.
Hydroporus sp.
1
Colymbetes sp.
Gyrinidae
Gyrinus sp.
Hydrophilidae
Helophorus (s.s.) splendidus Sahlb.
H. (Gephelophorus) sibiricus Motsch.
Hydrobius fuscipes F.
Other species (oth)
Leiodidae
Agathidium sp.
Staphylinidae
Deliphrum sp.
Tachyporus sp.
Lathrobium sp.
Quedius sp.
Staphylininae indeterminata
Curculionidae indeterminata
Lathridiidae indeterminata
Coccinellidae indeterminata
Coleoptera indeterminata
Table 3. continued.
326
BOREAS 33 (2004)
BOREAS 33 (2004)
327
deposits and the geomorphologic situation, it was not
possible to sample one continuous section; therefore
samples were taken from thermokarst mounds (baydzharakhs) in which deposits remain in situ after melting
of the surrounding ice wedges.
A standard HF technique was used for pollen
preparation (Berglund & Ralska-Jasiewiczowa 1986).
At least 200 pollen grains were counted in every
sample. The relative frequencies of pollen taxa were
calculated from the sum of the terrestrial pollen taxa.
Spore percentages are based on the sum of pollen and
spores. The relative abundances of reworked taxa
(Tertiary spores and redeposited Quaternary pollen)
are based on the sum of pollen and redeposited taxa, and
the percentages of algae are based on the sum of pollen
and algae. The Tilia/TiliaGraph software (Grimm 1991)
was used for the calculation of percentages and for
drawing the diagrams. Diagrams were zoned by visual
inspection.
Samples for beetle remains were sieved through a
0.5 mm (samples marked with B) and 1 mm (samples
marked with R) mesh. Originally, the R-marked
samples were intended to be used for rodent analyses,
but only a few rodent remains were found. The sample
size varied from 40 kg (for detritus-rich samples) to
200 kg (for samples containing few plant and insect
remains). Later, the insect remains were picked
manually under a binocular microscope.
Samples for chironomid analysis were mixed with
water, but were not sieved through a mesh. The analysis
followed methods outlined in Walker (2001). Taxonomic identification was carried out followed Wiederholm (1983) and Makarchenko & Makarchenko (1999).
Samples for testate amoebae analysis were sieved
through a 0.5 mm mesh and testate amoebae shells were
concentrated with a centrifuge. A drop of suspension
was placed on the slide, and then glycerol was added.
Normally, five subsamples were examined at 200–400
magnification with a light microscope.
Eight samples from selected profiles were dated by
the infrared stimulated luminescence (IRSL) technique
(Table 1). IRSL has already been successfully applied
for dating Late Quaternary deposits in the Lena Delta
(Krbetschek et al. 2002; Schirrmeister et al. in press).
The additive dose protocol was used for calculation of
the palaeodose (Aitken 1998). The samples, each
divided into 48 aliquots, were stepwise radiated
artificially with a Sr/Y b-irradiator. After irradiation
the samples were heated at 140°C for 48 h to remove the
unstable components of the luminescence signal. The
IRSL measurements were carried out using a Risø TL/
OSL DA12 automated luminescence reader (Risø
National Laboratory, Denmark). Luminescence stimulation was performed at a wavelength of 880 nm with an
optical power of 40 mW cm 2. The IRSL of the 410 nm
feldspar emission-peak (Krbetschek et al. 1997) was
measured using a 410/10 nm FWHD interference bandpass optical filter (Andover Corp.). For each sample,
natural normalization (0.1 s short-shine measurements
of natural signal), final measurement (100 s shine-down
measurements) and fading tests (0.1 s short-shine
measurements repeated on the same aliquots after 2–3
months’ storage) were conducted. A saturation exponential luminescence versus additive-dose characteristics was fitted using the ANALYST software (Duller
2001). The measurements were normalized by the
natural short shine signal and a late-light subtraction
was applied. The plateau-test (palaeodose versus
stimulation time) was applied to obtain information
about the bleaching level at the time of deposition
(Aitken 1998). Generally, the luminescence signals
were close to saturation. All samples show good
plateaus with constant palaeodoses versus increasing
stimulation time. The growth-curve fit was repeated for
the final palaeodose and error determination using the
integral values of the plateau. The dose-rate determination was performed by low-level high-resolution
gamma spectrometry. For the dose-rate calculation,
the natural radionuclides, cosmic radiation values and
water/ice contents were used. The software of Grün
(1992) based on procedures from Aitken (1985) was
used to calculate ages and error bars.
Another dating technique used for peaty sediments at
this study site is the 230Th/U method. The results
obtained were published by Schirrmeister et al. (2002b).
As the general stratigraphy of the subsampled profiles
was not clear in the field and previously published age
determinations were controversial, some selected plant
remains from the investigated profiles were also
collected for AMS radiocarbon dating at the Leibniz
Laboratory, Kiel (Table 2). The obtained ages are close
to or beyond the limit of 14C method and not
comparable with the 230Th/U and IRSL ages, nor with
geologically expected ages according to the stratigraphical positions of the samples in the outcrops. It is
possible that some of the AMS-dated organic matter
was removed by cryoturbation or by thermoerosional
processes. Therefore, no 14C dates have been used for
age estimation of the investigated deposits, which were
considered to be pre-Eemian and Eemian.
A total of 10 oriented samples (each in 6 subsamples)
from 3 profiles of units I and II were collected for
palaeomagnetic analyses. For the sampling, a 45-mm
sheet-steel cube with flat surfaces has been used. The
samples were stored in special 24 24 mm cardboard
boxes. The palaeomagnetic analyses were carried out at
the Laboratory of Main Geomagnetic Field and Magnetic Petrology, Institute of Physics of the Earth,
Russian Academy of Sciences.
The best modern analogue (BMA) method (Guiot
1990) was used to reconstruct climate characteristics
from the pollen spectra attributed to the Eemian. The
method has recently been applied to lateglacial and
Holocene pollen records from the Russian Arctic
(Andreev et al. 2003a, b, 2004). The accuracy of the
BMA method in comparison with other pollen-based
328
BOREAS 33 (2004)
Fig. 4. Palaeomagnetic
characteristics of sections
R1730, R1785 and R850.
reconstruction approaches is discussed in Andreev et al.
(2003b). In the present study, the same reference data
sets and calculation techniques as described in Andreev
et al. (2003a, b, 2004) were used. Mean July temperature and the annual sum of mean-day temperatures
above 5°C (GDD5) have the most definitive effect on
Arctic vegetation (Kaplan 2001) and are reconstructed
from surface pollen spectra from the Russian Arctic
with the highest confidence (Andreev et al. 2003a, b).
Results
Section R17
The 570-cm R17 section largely consists of old Ice
Complex silty to sandy deposits with some smaller
pebbles and peat inclusions covered by loess-like silty
deposits (Fig. 3). The sample from the periglacially
reworked Palaeogene weathering crust (80 cm a.s.l.)
contains no pollen. Pollen spectra from deposits above
can be divided into three pollen zones (Fig. 3). PZ-I
consists of one sample from 160 cm a.s.l. and is notable
for its low pollen concentration (5000 grains per cm3)
and large amounts of reworked Pinaceae. The spectrum
is dominated by Poaceae and Cyperaceae with some
other herb pollen (Caryophyllaceae, Cichoriaceae,
Artemisia). PZ-II (c. 170–640 cm a.s.l.) is characterized
by significantly higher pollen concentration (up to
35 000 grains per cm3) and very low presence of
reworked Pinaceae pollen. PZ-III (c. 640–670 cm
a.s.l.) is similar to PZ-I.
The sample R17-R4 (420 cm a.s.l.) from a nearbysituated (less than 5 m) subsection contains few beetle
remains, mostly mesic tundra species and species from
typical and arctic tundra habitats (Table 3). There is
only one typical tundra-steppe species, Morychus
viridis, a habitant of the so-called sedge heaths
(xerophilous Carex argunensis and Polytrichum piliferum dominated associations). Sediments from 450–
480 cm a.s.l. (sample R17-B2) are richer in insect
remains. The beetle fauna is dominated by mesic tundra
species (52%) and species from typical and arctic tundra
habitats (22%), but also includes habitants of dry tundra
(12%). There are single remains of the meadow-steppe
species, Coniocleonus sp. and the sedge-heath Morychus viridis. The sample R17-B1 (520 cm a.s.l.)
contains only remains of one typical tundra species
and one species from dry tundra habitat (Table 3). The
sediments from another nearby-situated section,
R1730 (R3 from 320 cm and R2 from 360 cm a.s.l.)
also contain species from dry, arctic, mesic tundra and
sedge heaths habitats (Table 3).
Two IRSL dates, 134 22 ka (Lya-2, 500 cm a.s.l.)
Fig. 5. Cryolithological structure and pollen percentage diagram of section R850 (for legend, see Fig. 3).
BOREAS 33 (2004)
329
330
BOREAS 33 (2004)
Table 4. List of testate amoebae species, varietetas and forms found in the R8 50 section.
Taxa name
Arcella arenaria v. compressa, A. discoides v. scutelliformis, Centropyxis aerophila, C. aerophila v. sphagnicola, C. aerophila v. grandis,
C. aerophila v. minuta, C. cassis, C. constricta, C. constricta v. minima, C. discoides, C. elongata, C. gibba, C. ovata cf.,
C. plagiostoma, C. plagiostoma f. A (major), C. plagiostoma f. B. (minor), C. platystoma, C. sylvatica, C. sylvatica v. microstoma,
C. sylvatica v. minor, C. sp., Cyclopyxis eurystoma, C. eurystoma v. parvula, Plagiopyxis minuta, Heleopera petricola, H. petricola v.
amethystea, Nebela bohemica, N. carinata, N. collaris, N. parvula, N. penardiana, N. tincta, N. tincta v. major, Difflugia ampululla,
D. acuminata, D. bryophila, D. decloitrei, D. difficilis, D. elegans, D. glans, D. globularis, D. globulosa, D. globulus, D. lanceolata,
D. leidy, D. limnetica, D. lucida, D. mamillaris, D. manicata, D. microstoma, D. minuta, D. molesta, D. paulii, D. penardi,
D. petricola, D. pristis, D. oblonga, D. teres, D. sp., Lagenodifflugia vas, Phryganella acropodia, Ph. acropodia v. australica cf.,
Quadrulella elongata, Q. scutellata, Q. symmetrica, Q. symmetrica v. longicollis, Tracheleuglypha acolla, Euglypha ciliata f. glabra,
E. laevis, E. strigosa f. glabra, Difflugiella apiculata
and 77 14 ka (Lya-3b, 750 cm a.s.l.) from the upper
part of the R17 section (Table 1) are in a good
agreement and do not contradict the suggested Saalian
age of the lowest deposits (Schirrmeister et al. 2002b).
However, organic matter of one sample located between
both IRSL samples was 14C dated to 36.51 0.96/
0.86 ka BP (Table 2).
Samples from section R1730 (Pm1 at 400 cm, Pm2
at 370 cm and Pm3 at 350 cm a.s.l.) and from another
nearby-situated section R1785 (Pm9 at 230 cm and
Pm10 at 240 cm a.s.l.) were collected for palaeomagnetic analyses (Fig. 4). Two samples show reversed
polarity, whereas the other three show intermediate
values. These may be associated with the location of
Fig. 6. Rhizopod percentage diagram of section R850.
these samples within the transition zone between
normal and reversed polarities in the section (Fig. 4).
Section R850
The 300-cm R850 section predominantly consists of
peat deposits within the old Ice Complex deposits and is
covered by loess-like silty deposits (Fig. 5). The pollen
diagram is divided into two pollen zones (Fig. 5). Pollen
zone I (PZ-I, 50 to c. 280 cm a.s.l.) is notable for its very
high pollen concentration (up to 80 000 grains per cm3)
and very low presence of reworked pollen. Poaceae with
a few Cyperaceae dominate the pollen spectra. In
contrast, PZ-II (c. 280 to 300 cm a.s.l.) consists of one
Fig. 7. Cryolithological structure and pollen percentage diagram of section R1440 (for legend, see Fig. 3).
BOREAS 33 (2004)
331
Fig. 8. Cryolithological structure and pollen percentage diagrams of section R985 (for legend, see Fig. 3).
332
BOREAS 33 (2004)
BOREAS 33 (2004)
333
sample from 300 cm a.s.l. and is notable for its
relatively low pollen concentration (5100 grains
per cm3), a relatively high content of Pediastrum and
large amount of reworked Pinaceae pollen. The
spectrum is dominated by Poaceae and Cyperaceae
pollen in this zone.
Rhizopod palaeocoenoses studied in the old Ice
Complex unit (Fig. 6) show a high diversity of species,
with 71 species, varietetas and forms found in the
section (Table 4). Although hydrophilous, eurybiotic
and soil species dominate the palaeocoenoses, almost
all samples also contain sphagnophilous species. Such a
species composition indicates wet mesotrophic conditions during the peat accumulation. The silty-sandy
sediments (250 cm a.s.l.) contain only a few remains of
eurybiotic Centopyxes constricta.
A 230Th/U date, 200.9 3.4 ka (117–140 cm a.s.l.),
indicates a Saalian age (Marine Isotope Stage 7) for the
peat deposits (Schirrmeister et al. 2002b). This peat was
also 14C dated to >53.25 ka BP. Plant remains collected
from the overlying aquatic loess-like silty sand were 14C
dated to 49.81 3.15/ 2.26 ka BP.
Additionally, the following samples were collected
for palaeomagnetic analyses: Pm4 at 250 cm, Pm5 at
280 cm, Pm6 at 310 cm, Pm7 at 350 cm and Pm8 at
420 cm a.s.l. Three samples have normal magnetization,
whereas two have a reversed magnetization (Fig. 4).
According to the 230Th/U age determination of the peat
lens below, the reversion of the magnetization can be
interpreted as the Biwa I event (180 ka).
sample is dominated by mesic tundra species (Pterostichus (Cryobius) brevicornis, P. (Cryobius) spp., P.
(Steroperis) costatus, P. (Steroperis) agonus, Tachinus
arcticus) and species from typical and arctic tundra
habitats (Chrysolina tolli, Ch. subsulcata, Ch. wollosowiczi and Isochnus arcticus). There are also a few
remains of aquatic, shrub, wet and riparian habitat
species. The R6 sample is similar to R5, but there are
also remains of meadow-steppe Coniocleonus sp.
Unfortunately, the IRSL sample collected from the
R1440 section is not yet dated, while one 14C age of
this deposit is 50.11 2.95/ 2.15 ka BP.
Section R985
The 270-cm R985 section consists of two sedimentologically similar, but cryolithologically different parts
of loess-like silty deposits. The lower part has a massive
cryostructure and the upper part is ice-banded (Fig. 8).
The pollen spectra are dominated by Poaceae and
Cyperaceae pollen with few other herbs (mostly
Caryophyllaceae). The pollen concentration is low (up
to 2000 grains per cm3). In addition, high amounts of
Pediastrum and reworked Pinaceae were observed.
and 77 19 ka (Lya-9, 1020 cm a.s.l.), obtained from
the section are in a good agreement and point to a
Middle–Early Weichselian age. A 14C age of 49.2 2.4/
1.85 ka BP from the sample at 900 cm a.s.l. does not
strongly contradict the IRSL dates.
Section R1440
A similar sequence of the old Ice Complex deposits and
aqueous loess-like deposits was studied in the 330 cm
section R1440 (Fig. 7). The pollen diagram can be
subdivided into two PZs (Fig. 7). PZ-I (470–560 cm
a.s.l.) is notable for its very high pollen concentration
(up to 115 000 grains per cm3) and very low presence of
reworked pollen. The spectra are dominated by Poaceae
and Cyperaceae pollen with few other herbs (mostly
Caryophyllaceae). Samples from PZ-1 also contain lake
and lake-bog diatoms: Eunotia lunaris v. subarcuata, E.
gracilis, E. praerupta, E. exigua, E. suecica, Diatoma
vulagre v. ovalis, Stauroneis anceps, Pinnularia borealis, Hantzschia amphioxys, Navicula pupula, N.
mutica, N. cf. bacillum (A. Bryantseva, pers. comm.).
The pollen concentration is significantly lower (up to
7300 grains per cm3) in PZ-II (c. 520–800 cm a.s.l.).
The zone is characterized by the dominance of Poaceae
and Cyperaceae pollen with some Caryophyllaceae and
Cichoriaceae. In addition, a relatively high content of
green algae (Botryococcus and Pediastrum) was
observed in this zone, as well as large amounts of
reworked Pinaceae.
The samples from a nearby section R1430 (R5 at
400 cm and R6 at 440 cm a.s.l.) were investigated for
insect remains (Table 3). The insect fauna of the R5
Section R1850 (Bj11–Bj13)
Overlapping profiles of two closely situated thermokarst
mounds (Bj11 and Bj13) were combined into one
section (Fig. 9). The sediments, as in the R985
section, consist of two sedimentologically similar, but
cryolithologically different units of loess-like silty
deposits separated by a large ice wedge. The pollen
diagram is divided into two subzones (Fig. 9). The PZIa (1190–1375 cm a.s.l.) is notable for the higher
content of Poaceae pollen, while PZ-Ib (1375–
1430 cm a.s.l.) contains higher amounts of Cyperaceae
pollen. The pollen concentration is very low (up to 2600
grains per cm3) in both subzones. In addition, a
relatively high content of reworked Pinaceae was
observed in both subzones.
An IRSL date, 57 10 ka (Lya-4, 1290 cm a.s.l.),
shows the Zyryanian (Early Weichselian) age. Another
IRSL sample (Lya-5, 1120 cm a.s.l) was not datable,
hence no age could be determined. This sample was
characterized by a strong radioactive disequilibria and
very high ice content, resulting in difficulties with dose
rate determination. Plant remains collected near the
IRSL sample Lya-4 (subsection Bj11) were 14C dated
to 44 3.43/ 2.39 ka BP, which does not contradict
the IRSL age. Plant remains from two other samples
334
BOREAS 33 (2004)
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335
336
BOREAS 33 (2004)
Table 5. List of testate amoebae species, varietetas and forms found in the Eemian deposits of the Zimov’e key site. Ecological preferences are
according to Chardez (1965): sh – Sphagnum, m – green moss, s – soils, w – water.
Species
Dominated ecological groups
Arcella arenaria v. compressa
Centropyxis aerophila
C. aerophila v. grandis
C. aerophila v. minor
C. cassis
C. constricta
C. constricta f. minor
C. ecornis (sensu Ogden, Hedley, 1980)
C. elongata
C. plagiostoma
C. plagiostoma minor
C. sylvatica
C. sylvatica v. minor
Cyclopyxis eurystoma
C. eurystoma v. parvula
Plagiopyxis callida f. grandis
Nebela tincta
Schoenbornia humicola
sh
m/s
w
w/m
w/m
w
w
w
w
s
s
w/sh/m/s
sh/s
w/sh
s
w/sh/m/s
sh/m/s
s
(subsection Bj13) were radiocarbon dated to >44.16 ka
BP and >54.05 ka BP (Table 2).
Section R2260
The 400-cm section consists mostly of fine-bedded
sands and silty sands overlaid by an ice-wedge cast
horizon filled with lacustrine silty deposits containing
L14-S2, 420
L14-S4, 540
R2260-S5, 300
w/s
w/m/s
w/s//sh/
3
13
1
2
3
6
16
1
2
2
2
1
1
2
2
2
1
5
3
16
15
1
1
10
small peat inclusions and shrub remains (Fig. 10).
Pollen spectra are grouped into three diagrams according to their origin and stratigraphical position (Fig. 10).
Diagram A (100–400 cm a.s.l.) consists of pollen
spectra from the silty sands below the ice-wedge casts.
The pollen spectra are dominated by Poaceae and
Cyperaceae pollen with few pollen of other herbs
(Caryophyllaceae, Asteraceae, Artemisia). Relatively
Table 6. Chironomid taxa (%) identified in the L1230 and R2260 sections. single chironomid head capsules.
Taxa
Bryophaenocladius
Chaetocladius
Corynoneura scutellata-type
Cricotopus/Orthocladius
Hydrobaenus
Limnophyes/Paralimnophyes
Metriocnemus/Thienemannia
Parakiefferiella bathophila (Kieffer)
Paraphaenocladius
Psectrocladius (P.) sordidellus-type
Smittia
Chironomus plumosus-type
Polypedilum
Sergentia coracina (Zetterstedt)
Stictochironomus
Zavrelia
Stempellinella
Micropsectra
Paratanytarsus
Tanytarsus chinyensis-type
Tanytarsini
Pentaneurini
Chironomidae undiff.
Total sum (n)
Concentration, head capsules g 1 DW
L1230, OS-56, 400
1.7
2.6
1.7
13.9
6.1
0.9
5.2
12.2
1.7
1.7
3.5
3.5
2.6
3.5
5.2
13.9
7.0
13.1
57.5
31.9
L1230, OS-56,430
R2260, S-5,300
2.8
4.3
5.6
2.8
17.0
11.3
2.8
5.6
2.8

8.5
2.8
2.8
5.6
2.8
2.8
5.6

14.1
53.5
5.5
4.0
0.3
BOREAS 33 (2004)
337
high contents of green algae (Botryococcus and
Pediastrum) and reworked indeterminable Pinaceae
also characterize diagram A. Three subzones are
distinguished, PZ-Ib (100 to c. 135 cm a.s.l.) differs
from PZ-Ia (100 cm a.s.l.) and PZ-Ic (c. 135–270 cm
a.s.l.) by large amounts of spores of a dung-inhabiting
fungi Sporormiella.
Diagram B (240–400 cm a.s.l.) consists of pollen
spectra from the lowest part of the ice-wedge cast. The
spectra are dominated by Poaceae and Artemisia pollen,
while the content of Cyperaceae is very low. Shrub
(Alnus fruticosa and dwarf Betula) pollen and spores of
coprophilous Sordariales fungi are also notable.
Diagram C (290–480 cm a.s.l.) consists of pollen
spectra from the upper part of the ice-wedge cast
horizon. Two pollen zones are distinguishable. PZ-I
(290–300 cm a.s.l.) includes only one sample characterized by high amounts of Betula sect. Nanae, Alnus
fruticosa pollen; Equisetum spores, fruit bodies of
Mycrothyrium (a fungi parasiting mostly on Carex
and Eriophorum) and a high pollen concentration.
Reworked Pinaceae and green algae colonies are almost
absent. The sample also contains shells of rhizopods
(Table 5) and few chironomid remains (Table 6). Soil
and eurybiotic species (Centropyxis aerophila, C.
constricta f. minor, Cyclopyxis eurystoma v. parvula,
Schoenbornia humicola) dominate, but sphagnophilous
Nebela tincta and Arcella arenaria were also found.
The chironomid remains consist of Tanytarsini undiff.
and semi-aquatic taxa Smittia and Limnophyes/Paralimnophyes.
The pollen spectra of PZ-II (300–480 cm a.s.l.) are
dominated by Poaceae and Cyperaceae pollen and
Equisetum spores with few pollen grains of other herbs.
Relatively high contents of green algae colonies and
reworked indeterminate Pinaceae also characterize this
zone.
The samples from the silty sands below the icewedge cast horizon (B13 at 120–150 cm and B14 at
240–270 cm a.s.l.) contain relatively few beetle
remains, mostly from dry tundra (Curtonotus alpinus,
Amara interstitialis), mesic tundra (Pterostichus (Cryobius) sp., Tachinus arcticus), typical and arctic tundra
(Isochnus arcticus) and sedge heath (Morychus viridis)
habitats.
The numerous beetle remains from the ice-wedge
cast (B15 at 250–280 cm and B16 at 400–430 cm a.s.l.)
are dominated by mesic tundra species (Pterostichus
(Cryobius) sp., P. agonus, Diacheila polita, Cholevinus
sibiricus, Olophrum consimile, Tachinus arcticus),
although species from dry (Notiophilus aquaticus),
sedge heath (Morychus viridis), meadow-steppe (Coniocleonus sp.) and steppe (Cymindis arctica, Chrysolina
brunnicornis bermani, Stephanocleonus eruditus, S.
fossulatus) habitats are also numerous. Some relatively
thermophilic meso-hygrophilous taxa were also found,
namely Diacheila polita, Olophrum consimile, Dorytomus imbecillus, Colymbetes dolabratus, Aegalia
kamtschatica, Deliphrum sp., Lathrobium sp., Tachyporus sp., Coccinellidae indet. and Lathridiidae indet.
and 102 16 (Lya-11 200 cm a.s.l.), do not strongly
contradict the suggested late Saalian age of the lowest
deposits. They are also in relatively good agreement
with a suggested Eemian age for the ice-wedge cast.
The possible explanation of the relatively young ages is
that the sediments below the ice-wedge casts (taberites)
were thawed during the existence of the Eemian lake
and refrozen. These processes possibly influenced the
physical and chemical properties of the samples causing
the young ages for the pre-Eemian sediments.
Section L14
The 350-cm L14 section predominantly consists of
lacustrine silty sediments filling an ice-wedge cast (Fig.
11). One sample was collected from the surrounding
silty sands, the rest from the ice-wedge cast. The pollen
spectra were divided into 3 PZs (Fig. 11). The PZ-I
(400 cm a.s.l.) includes only the sample from the
enclosing silty sands that are characterized by low
pollen concentration (2300 grains per cm3). The spectrum is dominated by Poaceae and Cyperaceae pollen
with few pollen of other herbs. Large amounts of
Sporormiella spores (dung-inhabiting fungi) and relatively high contents of green algae colonies (Botryococcus and Pediastrum) and reworked indeterminable
Pinaceae are also present. The pollen spectra from the
ice-wedge cast can be subdivided into two PZs. PZ-II
(300 to c. 360 cm a.s.l.) is distinguished by domination
of Artemisia and Poaceae pollen and a low content of
Cyperaceae pollen. In addition, a relatively high amount
of Betula and Alnus fruticosa pollen and spores of
coprophilous Sordariales fungi were observed. The
pollen spectra of PZ-III (c. 360–540 cm a.s.l.) are
dominated by Alnus fruticosa and Betula pollen. They
also contain a few rhizopod shells, mostly from soils
and eurybiotic species (Table 5). Hydrophilous Centropyxis ecornis and unidentified ostracods from the
lower sample may indicate an aquatic environment. The
upper sample contains mostly soil and eurybiotic
species, but moss and soil habitant, Centropyxis
elongata, is also present.
Two 14C ages of > 50 420 yr BP (420 cm a.s.l.) and
>50 880 yr BP (540 cm a.s.l.) confirm pre-Holocene age
of the sediments.
Section L1230
The 430-cm L1230 section consists mainly of an icewedge cast horizon filled with lacustrine clayey silt,
underlain by silty sands (Fig. 12). The pollen diagram
subdivided into two PZs (Fig. 12). PZ-I (350 to c.
390 cm a.s.l.) is from the lower silty sands and is
characterized by low pollen concentrations (up to 1200
pollen grains per cm3). The spectrum is dominated by
Fig. 11. Cryolithological structure and pollen percentage diagram of section L14 (for legend, see Fig. 3).
338
BOREAS 33 (2004)
BOREAS 33 (2004)
Poaceae and Cyperaceae pollen with few pollen of other
herbs. Large amounts of Sporormiella spores from
dung-inhabiting Sordariales fungi and relatively high
contents of green algae colonies (Botryococcus and
Pediastrum) and reworked indeterminable Pinaceae are
also characteristic for the spectrum. The pollen spectra
from the ice-wedge cast can also be subdivided into two
subzones. The pollen spectra are dominated by Alnus
fruticosa and Betula pollen with a rather high pollen
concentration (5100–14 600 grains per cm3) in both
subzones. The lower subzone (c. 390–550 cm a.s.l.) is
notable for a higher content of Salix, while the upper
subzone displays a higher content of Artemisia and
Poaceae.
The sample from 400 cm a.s.l. contained numerous
caddis fly (Trichoptera) remains and chironomid head
capsules (Table 6). The sample from 430 cm a.s.l.
contained only few caddis fly remains and concentration
of chironomids is significantly lower. In both samples
the chironomid head capsules are well preserved and
identified to 22 taxonomic groups (Table 6). The
assemblages are characterized by a high percentage
(25–41%) of semi-aquatic Smittia, Limnophyes/Paralimnophyes, Chaetocladius, Bryophaenocladius, Paraphaenocladius
and
Metriocnemus/Thienemannia
associated with moss habitats. The littoral thermophilous taxa (Cricotopus/Orthocladius, Zavrelia, Psectrocladius sordidellus-type, Tanytarsus chinyensis-type,
Stempellinella, Polypedilum, Corynoneura, Hydrobaenus, Pentaneurini) associated with aquatic macrophytes
are also numerous (25–27%). The thermophilous taxon,
Chironomus plumosus-type dominates (8–12%) in the
sublittoral/profundal group. Only a few indeterminable
chironomid remains have been found in the sample
from 700 cm a.s.l.
The deposits below the ice-wedge casts (B18 at 350–
380 cm a.s.l.) contain a few beetle remains from
different habitats (Table 3). The lacustrine silts (B17
at 400–430 cm and B19 at 700–730 cm a.s.l.) contain
numerous beetle remains, mostly mesic tundra species
(up to 45%), but species from dry tundra (up to 19%)
and steppe (including sedge heath habitats) are also
numerous. Typical riparian and aquatic species are
common (up to 10% and 8%, respectively) as well.
Some relatively thermophilic species, such as Pelophila
borealis and Olophrum consimile, have also been
found.
determinations, as well as the palaeoecological studies
of the surrounding deposits, support this interpretation.
The palaeoecological evidences of interglacial conditions were found in ice-wedge casts and lacustrine
deposits (unit III). Organic remains in the ice-wedge
casts were 14C dated to minimal ages. The loess-like
flood-plain deposits of units IIa and IV enclose the
Eemian lake deposits of unit III.
Sediments of unit IIa were IRSL dated to 102 16
and 99 15 ka (Table 1). The deposits of unit IV were
IRSL dated between 77 14 and 57 10 ka. There are
also 14C dates from unit IV with ages younger than the
IRSL dates from the same unit, but there are also dates
with minimal 14C ages (Table 2). In some profiles from
the central part of the outcrop, a disturbed horizon
above unit I is noticeable. In the R17 profile it was IRSL
dated to 134 22 ka. This horizon is probably a sign of
local hiatuses between unit I and unit IV, indicating the
patch-like sedimentation during the Eemian. In general,
units II and IV strongly differ from the Ice Complex of
unit V in their facies properties.
Based on the radiocarbon ages, Meyer et al. (2002b)
suggested that the loess-like flood-plain deposits rapidly
accumulated at around 50 ka BP. It was assumed that
there is a sedimentation hiatus of about 150 ka between
unit I and the flood-plain deposits. The new IRSL ages
clearly show that the postulated hiatus occurred locally
and was much shorter in duration. In contrast to the
Bykovsky Peninsula outcrops (Schirrmeister et al.
2002a; Meyer et al. 2002a; Andreev et al. 2002a;
Bobrov et al. 2004), where a continuous sequence of
one depositional unit (Late Pleistocene Ice Complex) is
preserved, the studied outcrops on Bol’shoy Lyakhovsky Island represent a discontinuously formed
sequence of permafrost deposits covering a much longer
time period.
TL ages of unit I and II obtained by Arkhangelov et
al. (1996) and Arkhangelov (pers. comm.) are certainly
over the limit of the TL method for sediments of this
kind (Table 7). On the contrary, the TL ages from unit II
(Kunitsky et al. 2000) and from units III and IV (A. A.
Arkhangelov, pers. comm.) fit quite well within the age
range of interest in this paper. Insufficient bleaching of
the sediments during accumulation is a major problem
for thermoluminescence age determinations, and hence
can cause geochronological confusion. This may quite
certainly be excluded for the IRSL dating, as bleaching
of the measured signal is faster and more effective. The
plateau tests carried out on these samples indicate
sufficient bleaching. Thus, it is assumed that the
resetting of the IRSL signal of these deposits was
complete during the transport and accumulation process.
Discussion: palaeoenvironmental
reconstructions
The most important result of this study is the clear
evidence of humid and warm (interglacial) palaeoenvironmental conditions during an interval significantly older than the Holocene. This interval is most
likely the Kazantsevo (Eemian) stage. Most of the age
339
Facies development
Geochronological studies of deposits older than the
range of the radiocarbon method are still in progress,
Fig. 12. Cryolithological structure and pollen percentage diagram of section L1230 (for legend, see Fig. 3).
340
BOREAS 33 (2004)
BOREAS 33 (2004)
341
Table 7. Thermoluminescence ages from previous studies on the Bol’shoy Lyakhovsky Island.
Lab. no.
Unit, profile (altitude a.s.l., m)
Age (ka)
Source
RTL-821
RTL-822
RTL-741
RTL-740
RTL-742
RTL-755
RTL-757
RTL-758
RTL-753
RTL-756
RTL-754
RTL-750
RTL-751
RTL-752
Unit II, R1670, 1.7
Unit II, R1770, 2
Unit IIb, L9, 4.1
Unit IIb, R2340, 5
Unit II, R2340, 2
upper Unit IV, R0410, 25
lower Unit IV, R07, 6.6
lower Unit IV, R07?
lower Unit IV, R1170, 16
Unit III, R8, 12
Unit II, R710, 8
Unit I, R760, 2–2.5
Unit I, R760, 4.5
Unit I, R760, 1–1.5
35 10
36 10
61 15
96 26
114 28
57 15
110 28
113 28
122 30
136 30
360 90
950 250
951 240
980 250
Kunitsky (1998)
Kunitsky (1998)
Kunitsky (1998)
Kunitsky et al. (2000)
Kunitsky et al. (2000)
Arkhangelov (pers. comm.
Arkhangelov et al. (1996)
especially for permafrost deposits. Therefore, difficulties with age determinations cannot be excluded. The
14
C ages presented in Table 2 reflect the Late
Pleistocene (non-Holocene) age of the studied deposits.
Based on 14C ages of around 50 ka BP obtained from
grass roots from the aquatic loess-like deposits (unit
IV), it is proposed that during the Early Weichselian
sedimentological facies developed similar to the preEemian one. There are, however, no simple explanations for the younger 14C ages. Possibly, they were
caused by contamination during cryoturbation and
thermokarst processes.
In general, a complex differentiation of the permafrost facies during the different stages of palaeolandscape development is suggested. This results in the
coexistence of older and younger units (sedimentary
bodies) at the same altitudes, or even the presence of
older deposits at higher levels than younger sediments
nearby. The suggested reasons are local erosion and
further accumulation by thermokarst and thermoerosion
as well as by fluvial processes. Observations of modern
permafrost landscapes in the area indicate that relief
strongly varies within short distances. Various periglacial forms (e.g. alas depressions, thermokarst lakes,
thermoerosional valleys, small rivers and Ice Complex
remains) coexist within a distance of a few hundred
metres or less. A similar situation is postulated for the
area during the Pleistocene, especially for the interstadial periods. During such periods, accumulation
often takes place in depressions only, whereas on
elevated areas erosion occurs or stable surfaces are
formed. This pattern produces a patch-like sedimentation with local hiatuses. Additional factors causing a
complicated geology are the strongly dislocated preQuaternary basement as well as neotectonic activities in
the region. The proposed stages of landscape development in the area are presented below.
1. In the early Pleistocene, the basement was covered
by a thick layer of so-called cryogenic elluvium
2.
3.
4.
5.
1998)
1998)
1998)
1998)
1998)
1998)
(deposits of periglacially reworked Palaeogene
weathering crust).
During the Middle Pleistocene (Saalian) the palaeorelief formed by basement structures was filled with
old Ice Complex deposits (unit I), resulting in the
formation of a relatively flat plain without strong
geomorphological differences.
The overlying loess-like silty sands of unit II reflect a
change of the facies. It is proposed that both subunits
(a and b) were accumulated on a flood-plain with
shallow lakes at the end of the Taz (Saalian) time.
The local stratigraphical name of these deposits is the
Kuchchugui Suite.
During the Eemian (Kazantsevo) stage, ice wedges of
unit II were thawed due to thermokarst processes.
The thermokarst depressions were subsequently
filled with lacustrine deposits (unit III). Strong
erosion processes took place during this stage. A
frequently observed reworking horizon covering the
ice wedges of the old Ice Complex unit reflects this
erosion, which was probably caused by seismotectonical events provoking a reorganization of the runoff
regime. The deposits were then eroded and redeposited in local depressions and valleys several times,
resulting in the facies nesting described above.
Loess-like deposits of unit IV accumulated at the
beginning of the Zyryanian (Early Weichselian)
stage. These deposits are sedimentologically similar
to the pre-Eemian unit IIa (they differ in their icebanded cryostructure and the absence of peat inclusions) and they probably consist of reworked material
from unit IIa.
The Saalian (Taz) environment
The age of the lowermost unit I is still indistinct.
According to the 230Th/U date from the R850 section,
peat accumulated c. 200 ka BP. This age seems to be
reliable, as frozen peat is a closed system for uranium
342
and thorium (Schirrmeister et al. 2002a). It is also in
good agreement with the upper Middle Pleistocene age
suggested by Romanovskii (1958b). On the contrary,
the TL dates obtained by Arkhangelov from unit I
(Table 7) are not reliable, since they are far beyond the
TL dating range limit for these kinds of sediments. TL
ages up to 300 ka are reliable only for polymineralic
fine-grained samples (Zöller et al. 1988; Shingvi et al.
1989). Although TL ages up to 400 ka are possible for
coarse-grained potassium feldspar samples, large errors
occur for ages older than 120 ka (Mejdahl 1988; Huett
& Jaeck 1989).
Palaeomagnetic investigations showed that samples
from the lowermost unit I are reversal magnetized.
Arkhangelov et al. (1996) believes that it is the
Jaramillo reversal event in the early Pleistocene.
However, according to the 230Th/U date, it can be
attributed to the Biwa I reversal event (c. 179–189 ka
BP; Nowaczyk & Antonow 1997).
A middle Saalian stadial (?). – The oldest pollen
spectrum from the studied deposits is PZ-I of R17 (Fig.
3), directly above the periglacially reworked remains of
the weathering crust. It reflects sparse grass-sedge
vegetation cover during this time. Relatively high
contents of Asteraceae and Cichoriaceae, as well as
large amounts of reworked pollen, indicate the presence
of disturbed soils and erosion of older deposits. Therefore, the reflected severe interval can be assigned to a
stadial during the middle Saalian time.
An interstadial c. 200–170(?) ka. – Pollen spectra from
the PZ-II of R17 (Fig. 3), PZ-I of R850 (Fig. 5) and
PZ-I of R1440 (Fig. 7) sections indicate that dense
grass-sedge tundra occupied the area after the severe
stadial time reflected in the lowest part of section R17.
Absence of typical cryoxerophitic taxa, high pollen
concentrations and low amounts of redeposited pollen
and spores indicate relatively warm and wet summers,
probably similar to (or even warmer than) modern ones.
Rhizopod remains from the old Ice Complex deposits
of section R850 (Fig. 6, Table 4) are numerous and
reflect a high taxa diversity (71 species, varietetas and
forms). The modern species diversity in the high Arctic
is lower. For example, only 45 taxa are found in the
modern habitats of Barents and Kara Seas coasts
(Beyens et al. 2000). The relatively well-investigated
rhizopod fauna of Spitzbergen consists of 48 taxa (Balik
1994). The high species diversity in the R850 section
may reflect a climate more favourable for the rhizopods
than today’s climate on the island. The rather stable
contents of palaeocoenoses in peat indicate a relatively
stable hydrothermal regime during the peat accumulation. A find of rare Quadrulella species is particularly
interesting. These species were previously not reported
from the region. Q. elongata is found only in Belgium
and Venezuela, while Q. scutellata was only reported
from North America (Chardez 1967), hence their
presence in the Saalian sediments shows that the
BOREAS 33 (2004)
distribution of these rare species was significantly
different from today.
Generally, pollen spectra of unit I are similar to the
pollen spectra from the upper part of the so-called
Kuchchugui suite. They accumulated in the vicinity of
the Laptev Sea coast during the end of the Middle
Pleistocene, and at some southern localities before the
last interglacial (e.g. Barkova 1970a, 1982). According
to Barkova (1970a, 1990), treeless grass-dominated
vegetation prevailed in the Laptev Sea region during
late Kuchchugui time.
The beetle fauna of the old Ice Complex sediments
(R17, R1730 and R1430 sections) is dominated by
mesic tundra species and species from typical and arctic
tundra habitats. The typical tundra-steppe beetles are
almost absent in the sediments. Only a few remains of
Coniocleonus sp. and Morychus viridis, which are
common in Late Pleistocene deposits and occur in
modern dry tundra habitats, were found (Kuzmina
2002).
Therefore, based on pollen, insect and rhizopod
records, it is assumed that this interval during the
middle Saalian time is an interstadial with relatively
warm and wet summers compared to modern conditions. Tundra habitats ecologically similar to modern
ones dominated the area. However, stable isotopes from
the ice wedges sampled in section R17 suggest severe
winter conditions during that time (Meyer et al. 2002b).
It is difficult to estimate the age of the interstadial.
Taking into consideration the stratigraphical sequence,
the IRSL and 230U/Th dates and the comparison of the
pollen records with the published late Kuchchugui ones,
a Saalian age for the lowest stadial and interstadial
sediments is assumed. Alternatively, according to
Arkhangelov et al. (1996) and Sher et al. (2002), these
sediments may have accumulated during the late
Pliocene/early Pleistocene. To accept their point of
view, it must be assumed that there is a continuous
hiatus between these early Pleistocene sediments and
the overlying Middle/Late Pleistocene sediments. This
hiatus must be several hundreds of thousands of years
long. However, the existence of such a hiatus requires
evidence. It is likely that only palaeontological remains,
if they can be found in situ, would help to determine the
age of the sediment.
It is also difficult to estimate the duration of the
interstadial, but if we take into consideration as an
example the duration of the Karginsky (Middle Weichselian) interstadial in Northern Siberia (e.g. Isaeva
1984; Lozhkin 1987; Anderson & Lozhkin 2001;
Andreev et al. 2002a, b), it may have lasted c. 30 ka
and ended c. 170 ka BP or earlier. Gavrilov & Tumskoy
(2001) also suggested that a relatively warm interval in
northern Yakutia during the Middle Pleistocene ended
about 170 (190) ka BP.
A late Saalian (Kuchchugui) stadial c. 170(?)–130 ka.
– The pollen spectra from PZ-III of R17 (Fig. 3), PZ-
Table 8. Environmental changes in the region c. 200–100 ka BP.
BOREAS 33 (2004)
343
344
II of R850 (Fig. 5), PZ-II of R1440 (Fig. 7), R985
(Fig. 8), R1850 (Fig. 9), diagram A of the R22 section
(Fig. 10), PZ-I of L14 (Fig. 11) and PZ-I of L1230
(Fig. 12) reflect a dramatic deterioration of the
environmental conditions compared with the previous
interstadial ones. The lower pollen concentrations may
reflect sparse grass-sedge vegetation cover during this
time and/or a dramatic decrease of pollen production.
Relatively high contents of Asteraceae and Cichoriaceae as well as large amounts of reworked pollen may
mirror the presence of disturbed soils and the erosion of
older deposits. The presence of green algae colonies (up
to 15%) suggests that sedimentation obtained in shallow
water conditions (probably, flood-plain environment).
A large amount of the dung-inhabiting Sordariales fungi
can be seen as an indication of grazing herds in the area
during that time. The sediments contain only a few
insect remains of species from dry, mesic, typical and
arctic tundra habitats. The very low presence of insect
remains is also evidence of the unfavourable environmental conditions and/or unfavourable conditions for
insect preservation.
The reconstruction of an extremely cold climatic
interval during the late Saalian (Kuchchugui), based on
the palaeoecological data, is also supported by the
isotopic analyses of the Kuchchugui ice wedges (Meyer
et al. 2002b). It can be concluded that an interval with
severe environmental conditions occurred at the end of
the Middle Pleistocene.
As with the earlier interval, the duration of the stadial
is difficult to determine. Considering the suggested
duration of the interstadial described above, and the
interglacial character of the pollen spectra from overlying ice-wedge casts, it is estimated that the stadial
began c. 170 ka and ended c. 130 ka BP, shortly before
the last interglacial.
A TL date obtained by Arkhangelov from Unit IIa of
360 90 ka BP (Table 7) is not reliable when taking
into consideration the dating limit of the TL method. On
the contrary, a TL date of 136 34 ka BP obtained
from ‘blue lacustrine sediments’ (grey lacustrine sediments from unit III?) fits well with the suggested late
Saalian age of the stadial and the Eemian (Kazantsevo)
age of the interstadial.
The Eemian (Kazantsevo) c. 130–110 ka. – Pollen
spectra from the diagram B of the R22 section (Fig.
10) and PZ-II of the L14 section (Fig. 11) reflect that
open plant associations with Poaceae and Artemisia
dominated vegetation at the beginning of the Eemian.
The high content of Artemisia pollen in the spectra may
indicate that disturbed and/or denuded soils were
common in the area. Alternatively, the dominance of
Poaceae and Artemisia in the spectra may indicate
steppe vegetation, which would correlate well with the
insect records. Although mesic tundra insects dominate
in the early Eemian sediments (ice-wedge cast samples
from R22 and L1230 sections), the relatively high
BOREAS 33 (2004)
presence of dry tundra and steppe (tundra-steppe)
species also indicates steppe or steppe-like habitats at
the beginning of the Eemian. The rather numerous
coprophilous Sordariales fungi spores may indicate the
presence of grazing herds at this time. Relatively high
contents of shrub (Alnus fruticosa, Salix, Betula nana)
pollen probably reflect that shrubs started to grow in
more protected places close to the site. The climate was
rather warm, resulting in the melting of the late Saalian
ice wedges.
High contents of Alnus fruticosa, Betula and Cyperaceae pollen and Equisetum spores are characteristic for
the PZ-I of the diagram C of the R22 section (Fig. 10),
PZ-II of the L14 section (Fig. 11) and of the L1230
section (Fig. 12). The low content of Ericales pollen is
characteristic for the Eemian sediments from the
Zimov’e River key section in comparison with Holocene ones (Andreev 2002a, b, and unpublished data).
This probably indicates a much drier environment
during the Eemian than during the Holocene. The
numerous remains of fossil Alnus fruticosa and Betula
nana s.l. twigs and trunks are also characteristic for the
middle Eemian deposits of the Zimov’e site. Species
from mesic and dry tundra habitats dominated the beetle
fauna. The studied interglacial deposits (Table 5) also
contain eurybiotic and soil rhizopods (e.g. Centropyxis
aerophila, Cyclopyxis eurystoma v. parvula, Schoenbornia humicola), as well as a few sphagnophilous ones
(Nebela tincta, Arcella arenaria v. compressa), while
hydrophilous species are absent. The species composition (dominance of Centropyxis species) indicates welldrained habitats with sufficient mineral nutrition. The
polymorphic character of the species (many species are
present not only by f. typica, but also subspecies,
varieties and f. minor) reflects frequent changes of the
hydrological regime in the area. For example, the
presence of Plagiopyxis callida f. grandis and Nebela
tincta together with numerous minor forms of Centropyxis species may indicate short-term dry conditions.
Chironomid assemblages and caddis fly remains reflect
environmental conditions of shallow lakes with a boggy
catchment area around the studied sites. The lakes were
likely characterized by an extensive development of
aquatic macrophytes in littoral zone and floating moss
mats along the lake shoreline. The high abundance of
thermophilous taxa may indicate relatively high summer air temperatures during this time. Thus, environmental records show that shrub tundra with numerous
lakes dominated the area during the Eemian optimum.
Unfortunately, the Eemian deposits on the Zimov’e
River key site survived only within the few buried icewedge casts and only a few fragmented interglacial
palaeoecological records were found, making the
reconstruction of short-term environmental fluctuations
during the interglacial more difficult. However, it can be
concluded that according to pollen and beetle data, the
steppe or tundra-steppe habitats were common in the
area at the beginning of the interglacial. Shrub commu-
BOREAS 33 (2004)
nities also grew in wetter places. Climate was warm and
relatively dry. The palaeoenvironmental records suggest that shrub tundra dominated the area later, during
the middle Eemian. The larger amounts of Poaceae,
Betula nana and Artemisia pollen, as well as higher
numbers of beetle remains from dry tundra and sedge
heath habitats in the upper part of the L1230 section,
may indicate some climatic deterioration during the
middle-late Eemian. The pollen spectra from PZ-II of
diagram C of the R22 section contains large amounts of
reworked Pinaceae pollen and few shrub pollen,
reflecting a significant deterioration of climate at the
beginning of the Eemian termination.
Thermal conditions reconstructed from pollen are
consistent with the qualitative interpretation of the
proxy records. The reconstructed July temperatures
vary from 7.8 to 9.6°C (taking into account the 0.9°/
1.3°C errors of the reconstruction). Hence, the July
temperatures were at least 4–5°C higher than today
during the climate optimum of the Eemian. Reconstruction of the effective temperatures above 5°C also
suggests that summers were warmer (GDD5 = 150–
230°C) than today (GDD5 = 0°C) during the optimum.
In the BIOME1 vegetation model (Prentice et al. 1992),
the reconstructed GDD5 values correspond to the tundra
vegetation. Temperature reconstruction from the pollen
spectra attributed to the early and late Eemian suggests
significantly colder (similar to present day) conditions
in comparison to the climate optimum.
The last interglacial (Kazantsevo, Krest-Yuryakh)
pollen records are relatively well known in northern
Yakutia (e.g. Rybakova 1962; Barkova 1970b; Rybakova & Kolesnikov 1983; Pirumova & Rybakova 1984;
Sher 1991; Lozhkin & Anderson 1995). Generally, such
records contain high percentages of tree and shrub
pollen, reflecting that forest or tundra-forest vegetation
dominated the northern Yakutia. As already pointed out
by Sher (1991), ‘traditionally, it was thought that during
“warm” stages, treeless tundra-steppe communities
were replaced by forest-tundra or taiga communities’.
However, such simple interpretations do not explain
how Pleistocene grazing mammal populations and
steppe insects survived during warm and wet stages
(Sher 1991). The new environmental records show that
dry steppe-like habitats existed during the Eemian in
northern Yakutia, especially in early and late Eemian,
but not during the Holocene. This may explain why
Pleistocene mammoth fauna survived during the last
interglacial but disappeared in the early Holocene.
the Early Weichselian stadial similar to the late Saalian
conditions.
Transition to Late Pleistocene stadial (Zyryanian,
Early Weichselian). – According to the IRSL ages
from the upper part of sections R17, R1850, R985
and TL dates from Unit IV (Table 7), the loess-like silty
sands have accumulated after the Eemian. Both
sedimentological and palaeoenvironmental records
reflect environmental conditions at the beginning of
345
Conclusions
The palaeoecological records from the Zimov’e site are
the first IRSL and 230Th/U dated records documenting
the environmental history of the Laptev Sea region
during the Taz (Late Saalian) and Kazantsevo (Eemian)
(Table 8). Pollen spectra and beetle fauna suggest that
wet grass-sedge tundra habitats dominated during the
interstadial c. 200–170(?) ka ago. Summers were
relatively warm and wet, while stable isotopes reflect
severe winter conditions.
The pollen spectra reflect sparser grass-sedge vegetation cover during the stadial, c. 170(?)–130 ka ago.
Environmental conditions were much more severe
compared with the previous interstadial.
Open Poaceae and Artemisia plant associations
dominated vegetation at the beginning of the Kazantsevo (Eemian). Some shrubs (Alnus fruticosa, Salix,
Betula nana) grew in more protected and wetter places.
Climate was fairly warm (similar to modern conditions)
during this time, resulting in the partial melting of Taz
(Saalian) ice wedges. Shrub tundra with Alnus fruticosa
and Betula nana s.l. dominated the vegetation in the
area during the middle Eemian climatic optimum, when
summer temperatures were 4–5°C higher than today.
The steppe-like habitats were rather widely distributed
during the last interglacial, especially during early and
late stages.
Acknowledgements. – We thank the participants, especially V.
Tumskoy and A. Derevyagin, of the expedition ‘Lena 1999' for their
generous help with collecting samples. The study was funded by the
German Ministry of Science and Technology through the German–
Russian science cooperation ‘Laptev Sea System’ and Helmholtz
Association of National Research Centres through the project
‘Natural climate variations from 10,000 years to the present day’.
S. Kuzmina and T. Kuznetsova thank RFBR (project 01-04-48930)
for support for insect and mammal studies. Pavel Tarasov thanks the
Alexander von Humboldt Foundation for financial support. The
chironomid study was supported via a grant awarded by DAAD to B.
Ilyashuk. Special thanks also go to Drs. Kevin Fleming for reviewing
the English and E. Taldenkova for identification of molluscs.
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